This invention relates to frequency synthesizers, and more particularly, to search and confirm frequency synthesizers (SCFS) containing two spectrum generators and a phase-locked loop.
The closest known prior art is disclosed in the Boelke patent (U.S. Pat. No. 3,694,766). Bielke discloses a frequency synthesizer having a single crystal oscillator coupled to a pair of dividers each of which generates a single frequency to be fed to a harmonic generator.
There are a number of inherent disadvantages to using frequency divider circuits in frequency synthesizers. Frequency dividers are expensive, complex, and have a relatively high D.C. power drain.
If it is desired to use the frequency synthesizer disclosed by Boelke to generate a frequency on the order of 1 gigahertz, the oscillator 10 shown in FIG. 1 of the Boelke patent must operate at a frequency approaching 1 gigahertz also. This is necessitated by the fact that the .DELTA. f frequency differential which is produced by the second divider 25 must be kept extremely small so that the harmonic generator output (designated by the formula n (f.sub.r + .DELTA. f)) when mixed with the nf.sub.r signal will be within the pass band of the lowpass filter 28. For operation in the gigahertz frequency range both divider 11 and divider 25 must divide the oscillator 10 output frequency down to a relatively low frequency (no more than a few megahertz) so that the frequency spacing between each harmonic will be small. This requires extremely high speed frequency dividers and utilizes considerable DC primary power. Although the Boelke apparatus might be highly acceptable for generating relatively low frequency output signals, it can be seen that for use in the UHF range that an apparatus of this design has serious disadvantages.